JP2006248842A - Furnace and method for drawing optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a furnace and a method for drawing an optical fiber which can suppress the deterioration of a heat resistant sealing member without using a chamber. <P>SOLUTION: The furnace 10 for drawing an optical fiber according to this invention draws an optical fiber preform P that is melted by heating in a furnace core 13 while purging the inside of the furnace core 13 with an inert gas G1, wherein there are provided a heat resistant sealing member 41 that has an annular ring-like shape and is located at an upper opened end of the furnace body for drawing the optical fiber and that seals the gap between the furnace body for drawing the optical fiber and the optical fiber preform P, an upper partition 34 having a through-hole 34c for passing the optical fiber preform P, and an antioxidant gas supply means for supplying the antioxidant gas G2 into a small chamber 35 that is an inner space of the upper partition 34. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical fiber drawing furnace and an optical fiber drawing method, and more particularly to an optical fiber drawing furnace and an optical fiber drawing method for drawing a large and long optical fiber preform. .

  In general, an optical fiber is manufactured using a manufacturing apparatus as shown in FIG. In this manufacturing apparatus, first, in the drawing furnace 80, the optical fiber preform 111 is heated and melted and then drawn vertically downward, whereby the optical fiber 112 is drawn from the furnace outlet 95. The drawing furnace 80 mainly includes a core tube 91 in which the optical fiber preform 111 is accommodated, a heater 94 for heating and melting the optical fiber preform 111, and an inner core in which the drawn optical fiber 112 is passed. And a tube 92. A core 93 is formed by the internal space of the core tube 91.

  The extracted optical fiber 112 is cooled by blowing a cooling gas in the cooling pipe 84 after the outer diameter is measured by the outer diameter measuring device 83. Then, after coating the resin around the optical fiber 112 in the coater 85 (for example, ultraviolet curable resin), the resin is cured by passing the optical fiber 112 through the resin curing furnace 86. As a result, the optical fiber 113 is obtained. The cooling, resin coating, and resin curing steps are repeated as appropriate. Thereafter, the traveling direction of the optical fiber 113 is changed by the turn pulley 87, and is taken up by the winder 89 through the take-up capstan 88.

  Since the drawing furnace 80 needs to heat the quartz-based optical fiber preform 111 to about 2000 ° C., ceramics such as high-purity carbon and zirconia are generally used as the material of the core tube 91 and the inner core tube 92. Used.

  When an optical fiber is manufactured using a drawing furnace having a core tube 91 and an inner core tube 92 made of high purity carbon, in order to prevent oxidation of the core tube 91 and the inner core tube 92 in the core 93, the core The inside of the core 93 is purged by the inert gas supplied into the 93. At this time, depending on the flow direction of the inert gas, the drawing furnace has an upflow type in which the inert gas G flows upward as shown in FIG. 9 and an inert gas G in the downward direction as shown in FIG. Broadly divided into flowing downflow types.

  In the case of the upflow type, a reduced diameter part (cylindrical member with a flange) 97 having a slightly larger diameter than the optical fiber preform 111 is provided on the upper portion of the core tube 91. The inert gas G is introduced from a gas inlet 98 provided below the drawing furnace and flows upward in the core 93, and then the gap between the optical fiber preform 111 and the reduced diameter portion 97 (hereinafter referred to as an upper gap). ) To the outside of the core 93. An exhaust port 99 provided with a valve 99a for adjusting the pressure of the inert gas G in the core 93 is appropriately provided above the drawing furnace.

  On the other hand, in the case of the down flow type, an annular heat-resistant sealing member 107 having a hole having substantially the same diameter as that of the optical fiber preform 111 is provided on the upper portion of the drawing furnace main body. The inert gas G is introduced from a gas inlet 108 provided above the drawing furnace, flows downward in the core 93, and then from a gap between the optical fiber 112 and the furnace outlet 95 (hereinafter referred to as a lower gap). The gas is exhausted out of the core 93. Below the drawing furnace, an exhaust port 109 provided with a valve 109a for adjusting the pressure of the inert gas G in the core 93 is appropriately provided.

  In general, when the optical fiber preform 111 is taken in and out of the core 93 of the drawing furnace, outside air may be mixed into the core 93. When this outside air reacts with carbon which is a constituent material of the core tube 91 when the optical fiber preform 111 is heated, it is oxidized and burned, and dust is generated. Further, when the optical fiber preform 111 is melted, dust is generated due to evaporation of quartz.

  In the upflow type, dust is exhausted together with the inert gas G from the upper gap. For this reason, there is a possibility that dust adheres to the surface of the optical fiber preform 111. Further, since a large amount of inert gas G is exhausted from the upper gap, a large amount of inert gas G is required to keep the inside of the core 93 at a positive pressure. In the down flow type, the dust is exhausted together with the inert gas G from the lower gap. For this reason, dust may adhere to the surface of the optical fiber 112 and the strength of the optical fiber 112 may be reduced.

  For the above problems, there is a drawing furnace having a structure combining the upflow type and the downflow type (hereinafter referred to as a composite type) (see, for example, Patent Documents 1 and 2). The drawing furnace described in Patent Document 1 includes an upper inner core tube and a lower inner core tube inside a core tube (outer core tube). The inert gas supplied from below the drawing furnace is exhausted from above the drawing furnace via the lower inner core tube and the upper inner core tube. Further, the inert gas supplied from above the drawing furnace is exhausted from below the drawing furnace through the space between the outer core tube and the upper inner core tube and the space between the outer core tube and the lower inner core tube. The

Japanese Patent No. 2760977 JP 2003-206155 A

  However, in the composite type drawing furnace, from the viewpoint of preventing dust from adhering to the optical fiber preform 111, it is necessary to secure a sufficient flow rate of the inert gas G flowing downward. A reliable gas seal is a problem. In recent years, in order to reduce the cost of optical fibers, the optical fiber preform has been increased in size (increase in diameter) and lengthened. Along with this, the amount of heat generated in the core 93 tends to increase. As a result, the heat resistant sealing member 107 shown in FIG. 10 is significantly deteriorated and oxidized regardless of the constituent material (metal or carbon). In order to prevent this thermal deterioration and oxidation, a method in which a chamber (vacuum chamber) is provided on the drawing furnace and the surroundings of the heat-resistant sealing member 107 are evacuated to shut off oxygen is considered. As the size and length of optical fiber preforms are increasing, inevitably a large chamber is required. However, the increase in the size of the chamber is naturally limited due to restrictions on the drawing furnace device structure and installation space.

  The object of the present invention created in view of the above circumstances is to provide an optical fiber drawing furnace and an optical fiber drawing method capable of suppressing deterioration of a heat-resistant sealing member without using a chamber. There is.

To achieve the above object, an optical fiber drawing furnace according to the present invention is an optical fiber drawing furnace for drawing an optical fiber preform heated and melted in the core while purging the inside of the core with an inert gas.
An annular heat-resistant sealing member that is provided at the upper opening end of the drawing furnace body into which the optical fiber preform is inserted, and that closes the gap between the drawing furnace body and the optical fiber preform;
An upper partition wall that surrounds and covers the heat-resistant sealing member and has an insertion hole for passing an optical fiber preform;
An antioxidant gas supply means for supplying an antioxidant gas into a small chamber that is an internal space of the upper partition;
It is equipped with.

  Here, the antioxidant gas supply means preferably includes a control device for controlling the supply amount of the antioxidant gas so that the oxygen concentration in the small chamber is 200 ppm or less. Moreover, it is preferable to comprise the heat-resistant sealing member with a felt material made of high purity carbon.

On the other hand, the optical fiber drawing method according to the present invention is an optical fiber drawing method for drawing an optical fiber preform heated and melted in the core while purging the inside of the core with an inert gas.
When the optical fiber preform is inserted from the upper opening end of the drawing furnace body, the optical fiber preform is heated and melted in the core, and then drawn.
In order for the inert gas not to leak from the gap between the drawing furnace main body and the optical fiber preform, the gap is closed with an annular heat-resistant sealing member, and the heat-resistant sealing member is covered with an upper partition, An antioxidant gas is supplied to the small chamber, which is the internal space of the upper partition, and the oxygen concentration in the small chamber is adjusted to 200 ppm or less.

  ADVANTAGE OF THE INVENTION According to this invention, when drawing an optical fiber, the outstanding effect that there is no possibility that the heat-resistant sealing member which performs the gas seal in the drawing furnace main body upper part may deteriorate is exhibited.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of the invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a schematic structural diagram of an optical fiber drawing furnace according to a preferred embodiment of the present invention.

  As shown in FIG. 1, an optical fiber drawing furnace 10 according to the present embodiment draws an optical fiber preform P heated and melted in a core 13 to produce an optical fiber OF.

  The core tube 11 is composed of a pipe material having an open end on the top and bottom, and a part in the longitudinal direction of the optical fiber preform P welded to the dummy rod R is accommodated in the upper open end. The inner space of the core tube 11 forms the core 13. The dummy bar R is provided so as to be movable in the direction of the arrow A1 (vertical direction in FIG. 1).

  A furnace shell 16 is provided so as to surround the core tube 11. A heater (heating means) 14 for heating and melting the optical fiber preform P is provided in the furnace shell 16. The heater 14 is disposed so as to surround the vicinity of the central portion in the length direction (vertical direction in FIG. 1) of the core tube 11. For example, the upper end of the core tube 11 is provided flush with the upper surface wall 16 a of the furnace shell 16, and the lower end of the core tube 11 is provided so as to protrude from the lower surface wall 16 b of the furnace shell 16.

  An inert gas supply means 32 is provided in the upper part of the optical fiber drawing furnace 10. More specifically, the cylindrical member 33 is provided so as to surround the core tube 11 in contact with the upper surface wall 16 a of the furnace shell 16. The cylindrical member 33 includes a cylindrical portion 33a and a flange portion 33b formed at a non-top wall side end (upper end in FIG. 1) of the cylindrical portion 33a. A first gas supply line (not shown) having a gas tank is connected to an inert gas ejection hole 33c formed in the cylindrical portion 33a, and the inert gas is introduced into the cylindrical portion 33a through the inert gas ejection hole 33c. G1 is ejected. At this time, you may form the inert gas ejection hole 33c opened to the perimeter of the inner peripheral surface of the cylindrical part 33a so that the inert gas G1 may be ejected from the perimeter of the inner peripheral surface of the cylindrical part 33a.

  An annular heat-resistant sealing member 41 having a hole 42 having a smaller diameter than the optical fiber preform P (substantially the same diameter as the optical fiber preform P) is provided on the upper portion of the flange portion 33b. The heat sealing member 41 provides a gas seal between the optical fiber preform P and the drawing furnace body. As shown in FIG. 4, the heat-resistant sealing member 41 is composed of a felt material disc 41 made of high-purity carbon having stretchability. For this reason, the hole 42 can follow the outer diameter variation of the optical fiber preform P.

  In addition, an upper partition wall 34 is provided above the flange portion 33b so as to surround and cover the heat-resistant sealing member 41. The upper partition wall 34 includes a large-diameter portion 34a on the flange portion side and a small-diameter portion 34c on the dummy rod side, and the large-diameter portion 34a and the small-diameter portion 34c are integrally provided via a reduced-diameter portion (stepped portion) 34b. . The small diameter portion 34c becomes an upper opening of the drawing furnace main body, and the optical fiber preform P is inserted through this portion.

  Connected to the upper partition wall 34 is an antioxidant gas supply means (not shown) for supplying the antioxidant gas G2 into a small chamber 35 which is an internal space thereof. The antioxidant gas supply means includes a control device that controls the supply amount of the antioxidant gas G2 so that the oxygen concentration in the small chamber 35 is 200 ppm or less, preferably 150 ppm or less.

  As a constituent material of the heat-resistant sealing member 41, any material can be used as long as the hole 42 can be expanded and contracted following the change in the outer diameter of the optical fiber preform P and the surface of the optical fiber preform P is not damaged. The felt material is not limited to high purity carbon. For example, various ceramic disk materials may be used.

  Further, the structure of the heat-resistant sealing member 41 is not limited to the structure in which the hole 42 is formed in the central portion of the disc material 41a as shown in FIG. For example, as shown in FIG. 5, even if the heat-resistant sealing member 51 has slits 53 (four slits extending radially from the center of the disk material in FIG. 5) 53 around the hole 52 of the disk material 51a. Good. Further, as shown in FIG. 6, a heat-resistant sealing member 61 having a laminated structure in which a plurality of heat-resistant sealing members 41 shown in FIG. 4 are stacked (in the case of four in FIG. 6) may be used. . Further, as shown in FIG. 7, a disk material having a hole 72 formed at the center is divided into multiple parts (in FIG. 7, the case of three parts is shown), that is, arc-shaped parts 71a, 71b, It may be a heat resistant sealing member 71 composed of 71c,... (In FIG. 7, the divided pieces 71a, 71b, 71c are shown).

  Examples of the constituent material of the core tube 11 include ceramics such as high-purity carbon and zirconia.

The inert gas G1 and the antioxidant gas G2 are preferably He gas having a large diffusion coefficient, but are not particularly limited thereto, and may be Ar gas or N ₂ gas. Moreover, both gas G1, G2 may be either the same kind or different kind.

  Next, an optical fiber drawing method using the optical fiber drawing furnace according to the present embodiment will be described.

  The core 13 of the optical fiber drawing furnace 10 shown in FIG. On the other hand, the inert gas G <b> 1 is supplied from above the optical fiber drawing furnace 10 via the first inert gas supply means 32. Further, an antioxidant gas G2 is supplied into the upper partition 34.

  At this time, since the supply amount of the antioxidant gas G2 is controlled by the control device of the antioxidant gas supply means, the oxygen concentration in the small chamber 35 is always kept at 200 ppm or less. Here, when the oxygen concentration in the small chamber 35 is more than 200 ppm, the heat-resistant sealing member 41 is thermally deteriorated and oxidized by excess oxygen contained in the atmospheric gas. As a result, in the worst case, a gap is generated between the heat-resistant sealing member 41 and the optical fiber preform P, and the sealing effect is impaired. However, by always controlling the oxygen concentration in the small chamber 35 to 200 ppm or less, the heat resistant sealing member 41 is not likely to be thermally deteriorated and oxidized, and the heat resistant sealing member 41 maintains the sealing effect for a long period of time. Can be made.

  Thereafter, the optical fiber preform P is melted and the optical fiber OF is drawn. Here, above the optical fiber drawing furnace 10, the gap between the drawing furnace main body and the optical fiber preform P is almost completely gas-sealed by the heat-resistant sealing member 41. Accordingly, almost the entire amount of the inert gas G1 flows downward through the gap between the core tube 11 and the optical fiber preform P and is guided into the core 13.

  On the other hand, when the dummy rod R is moved downward by a certain amount as the drawing progresses, the object to be sealed by the heat-resistant sealing member 41 shifts from the optical fiber preform P to the dummy rod R. Here, since the outer diameter of the dummy rod R is the same as the outer diameter of the optical fiber preform P, the gap between the drawing furnace body and the dummy rod R is almost completely covered by the heat-resistant sealing member 41 in this case as well. Gas sealed. In particular, when the welded portion (joint portion) between the optical fiber preform P and the dummy rod R is positioned at the heat-resistant sealing member 41, the welded portion is at a high temperature. The heat load at is very large. However, even in this case, the heat resistant sealing member 41 is not likely to be thermally deteriorated or oxidized by always controlling the oxygen concentration in the small chamber 35 to 200 ppm or less.

  As described above, by drawing the optical fiber OF using the optical fiber drawing furnace 10 according to the present embodiment, a high-temperature heat load acts on the heat-resistant sealing member 41 for a long time during drawing. However, there is no possibility that the heat-resistant sealing member 41 is thermally deteriorated and oxidized. The same applies to the case where a large and long optical fiber preform P that increases the amount of heat generated in the core 13 is used. Therefore, since the gas seal at the upper part of the drawing furnace main body can be surely performed during the drawing, the core 13 can be sufficiently obtained without increasing the flow rate of the inert gas G1 supplied from the inert gas supply means 32 so much. The purge inside can be performed. As a result, since the amount of the expensive inert gas G1 used can be reduced, the long optical fiber OF can be drawn at a low cost.

  Further, according to the optical fiber drawing furnace 10 according to the present embodiment, the main device members for preventing the heat resistant sealing member 41 from deteriorating are only the upper partition wall 34 and the antioxidant gas supply means. There is no need to provide a large and expensive vacuum chamber on the furnace body. Therefore, the optical fiber drawing furnace 10 according to the present embodiment can also be applied to an existing optical fiber drawing furnace in which a chamber cannot be installed due to restrictions on the apparatus structure and installation space.

  Next, a modification of the present embodiment will be described based on the attached drawings.

  A modification of the optical fiber drawing furnace of FIG. 1 is shown in FIGS. In addition, the same code | symbol is attached | subjected to the member similar to FIG. 1, and description is abbreviate | omitted about these members.

  In the present embodiment, as shown in FIG. 1, the case where the outer diameter of the dummy rod R and the outer diameter of the optical fiber preform P are equal is described as an example, but the present invention is not limited to this. Absent.

  For example, as shown in FIG. 2, the outer diameter of the dummy rod R may be smaller than the outer diameter of the optical fiber preform P. In this case, the dummy tube 21 is provided in the vicinity of the welded portion between the dummy rod R and the optical fiber preform P. The dummy tube 21 includes a disc portion 21a and a cylindrical portion 21b. The disc part 21a has an outer diameter larger than the inner diameter of the small diameter part 34c in the upper partition wall 34, and has a hole 22 in the central part. The inner diameter of the hole 22 is slightly larger than the outer diameter of the dummy rod R (substantially the same diameter as the dummy rod R), and the hole 22 serves as an insertion hole for allowing the dummy rod R to pass. The cylindrical portion 21b has an outer diameter that is the same diameter (or substantially the same diameter) as the outer diameter of the optical fiber preform P. You may form the peripheral part of the hole 22 of the disc part 21a, preferably the whole disc part 21a with the same material as the heat-resistant sealing member 41.

  When drawing is performed by the optical fiber drawing furnace 10 using the dummy rod R and the optical fiber preform P provided with the dummy tube 21, in the first half of the drawing process, the drawing furnace body and the optical fiber preform are used. The gap of P is gas sealed with the heat-resistant sealing member 41.

  Thereafter, when the dummy rod R is lowered as the drawing progresses, the disc portion 21a of the dummy tube 21 is seated on the small diameter portion 34c of the upper partition wall 34 at a certain stage as shown in FIG. The At this time, the open part (small diameter part 34c) of the upper partition 34 is closed by the disc part 21a, and the small chamber 35 is completely sealed. After the seating, even if the dummy rod R is further lowered, the disk portion 21a does not move by being held by the small diameter portion 34c, so the dummy tube 21 does not follow the dummy rod R and descend. Further, after this seating, the member that performs gas sealing on the upper portion of the drawing furnace main body is changed from the heat-resistant sealing member 41 that is in close contact with the optical fiber preform P to the disk portion 21a that is in close contact with the dummy rod R. Therefore, since the sealing of the core 13 and the small chamber 35 is maintained by the disc portion 21a even after a certain stage of the drawing process, there is no possibility that the heat resistant sealing member 41 is thermally deteriorated and oxidized.

  As described above, the present invention is not limited to the above-described embodiment, and it goes without saying that various other things are assumed.

  Next, although this invention is demonstrated based on an Example, this invention is not limited to this Example.

Example 1
The optical fiber was drawn using the optical fiber drawing furnace having the structure shown in FIG. As the optical fiber preform, a large diameter one having an outer diameter of 110 to 120 mm was used. Moreover, as the heat-resistant sealing member, the one having the structure shown in FIG. Further, the inner diameter of the small diameter portion in the upper partition was 130 mm. Further, nitrogen gas was used as an antioxidant gas supplied into the small chamber of the upper partition, and the flow rate was controlled to 70 L / min to adjust the oxygen concentration in the small chamber to 120 ppm.

(Example 2)
The optical fiber was drawn in the same manner as in Example 1 except that the optical fiber drawing furnace having the structure shown in FIG. 2 was used.

(Comparative Example 1)
The optical fiber was drawn in the same manner as in Example 1 except that the oxygen concentration in the small chamber was adjusted to 400 ppm.

(Comparative Example 2)
The optical fiber was drawn in the same manner as in Example 1 except that the oxygen concentration in the small chamber was adjusted to 1000 ppm.

  The heat-resistant sealing members in the optical fiber drawing furnaces of Examples 1 and 2 and Comparative Examples 1 and 2 were observed from before the drawing to the end of drawing.

  As a result, the heat-resistant sealing member in each optical fiber drawing furnace of Examples 1 and 2 was not deteriorated at all.

  On the other hand, in the optical fiber drawing furnace of Comparative Example 1, during the drawing, when the welded portion of the optical fiber preform and the dummy rod reaches the position of the heat resistant sealing member, the heat resistant sealing member is deteriorated. Progressed all at once, and the internal pressure of the core could not be maintained. When drawing was stopped at this stage and the heat-resistant sealing member was observed, the hole peripheral portion of the disk material disappeared, and the hole inner diameter increased from 105 mm to 123 mm.

  Further, in the optical fiber drawing furnace of Comparative Example 2, the heat-resistant sealing member was deteriorated in the preheating stage before the drawing was started, and the internal pressure of the core could not be increased to a predetermined pressure. When preheating was stopped at this stage and the heat-resistant sealing member was observed, the hole peripheral portion of the disk material disappeared, and the hole inner diameter increased from 105 mm to 110 mm.

  As described above, when drawing an optical fiber using the optical fiber drawing furnace according to the present invention, the oxygen concentration in the small chamber in the upper shell is controlled to 200 ppm or less, so that the heat-resistant sealing member can be used even after drawing. It was confirmed that no deterioration occurred.

1 is a schematic structural diagram of an optical fiber drawing furnace according to a preferred embodiment of the present invention. It is a figure which shows the modification of the optical fiber drawing furnace of FIG. FIG. 3 is a diagram when drawing is further advanced in FIG. 2. It is an expansion perspective view of the heat resistant sealing member in FIG. It is a modification of the heat-resistant sealing member of FIG. It is another modification of the heat-resistant sealing member of FIG. It is another modification of the heat-resistant sealing member of FIG. It is a whole schematic diagram of an optical fiber manufacturing apparatus. It is the structure schematic which shows an example of the conventional optical fiber drawing furnace. It is the structure schematic which shows the other example of the conventional optical fiber drawing furnace.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical fiber drawing furnace 11 Core tube 13 Core 34 Upper partition 34c Small diameter part (insertion hole)
35 Small chamber 41 Heat-resistant sealing member P Optical fiber preform OF Optical fiber G1 Inert gas G2 Antioxidant gas

Claims (4)

In an optical fiber drawing furnace for drawing an optical fiber preform heated and melted in the core while purging the inside of the core with an inert gas,
An annular heat-resistant sealing member that is provided at the upper opening end of the drawing furnace body into which the optical fiber preform is inserted, and that closes a gap between the drawing furnace body and the optical fiber preform;
An upper partition wall that surrounds and covers the heat-resistant sealing member, and has an insertion hole for passing an optical fiber preform;
An antioxidant gas supply means for supplying an antioxidant gas into a small chamber that is an internal space of the upper partition;
An optical fiber drawing furnace comprising:   2. The optical fiber drawing furnace according to claim 1, wherein the antioxidant gas supply means includes a control device for controlling an amount of supply of the antioxidant gas so that an oxygen concentration in the small chamber becomes 200 ppm or less.   The optical fiber drawing furnace according to claim 1 or 2, wherein the heat-resistant sealing member is made of a felt material made of high purity carbon. In the optical fiber drawing method of drawing the optical fiber preform heated and melted in the core while purging the inside of the core with an inert gas,
When the optical fiber preform is inserted from the upper opening end of the drawing furnace body, the optical fiber preform is heated and melted in the core, and then drawn.
In order for the inert gas not to leak from the gap between the drawing furnace main body and the optical fiber preform, the gap is closed with an annular heat-resistant sealing member, and the heat-resistant sealing member is covered with an upper partition, An optical fiber drawing method, wherein an antioxidant gas is supplied into a small chamber that is an internal space of the upper partition wall, and an oxygen concentration in the small chamber is adjusted to 200 ppm or less.

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